Abstract

The potential energy surface for the unimolecular ground state elimination/detachment reactions of vinylchloride (VCl) is studied with abinitio molecular orbital calculations. Using second order Mo/ller–Plesset perturbation (MP2) gradient optimizations and quadratic single and double configuration interaction including a triple contribution [QCISD(T)] single point calculations, many possible channels—three‐ and four‐center elimination reactions of HCl and H2, H, and Cl migrations, single atom detachments—are systematically examined. The overall barrier for the HCl three‐center elimination, 69.1 kcal/mol, and subsequent vinylidene rearrangement is lower than that for the four‐center elimination, 77.4 kcal/mol, the result being consistent with the most recent experiments. The H2 elimination, with a barrier of 97.2 kcal/mol and more difficult than the HCl elimination, also proceeds via a three‐center transition state, followed by an easy H migration from chlorovinylidene intermediate. The lowest energy path from VCl is the α‐H migration with a barrier of 68.8 kcal/mol, which gives a stable intermediate, α‐chloroethylidene, with an energy of 55 kcal/mol relative to VCl. This path cannot however proceed further because of a very high barrier for subsequent H2 and HCl elimination, but the return to VCl provides the easiest mechanism for H scrambling in VCl. The β‐chloroethylidene species is only a marginally stable intermediate and would not contribute to the reaction.